Quiz Questions and Solutions

Quiz Questions and Solutions Question 1: H2 O and ions cross biological membranes more readily than artificial lipid bilayers. This is because: 1. Artificial lipid bilayers are often made from only one type of phospholipid. 2. Biological membranes contain transport proteins that facilitate ion and water movement. (Correct Answer) 3. Artificial membranes are more permeable than biological membranes. 4. Biological membranes contain sterols as well as phospholipids. Solution: Biological membranes have specialized transport proteins like channels and carriers that facilitate the movement of water and ions, unlike artificial lipid bilayers which lack these proteins. For instance, aquaporins allow rapid water transport, and ion channels enable the selective passage of ions. Without these transport proteins, artificial membranes are less permeable to water and ions. Question 2: Which of the following statements about passive transport is FALSE? 1. Some passive transport gated channels require energy to open and close. 2. The direction of transport of solutes is driven by their electrochemical gradient. 3. Only ions are transported through passive transporters. 4. Passive transport can lead to an electrical potential across a membrane. Correct Answer: Some passive transport gated channels require energy to open and close. Solution: Passive transport does not require the expenditure of cellular energy (ATP). It relies on the concentration gradient of the molecules being transported. Channels involved in passive transport open in response to stimuli, such as voltage changes or ligand binding, without consuming ATP. Question 3: Secondary active transport requires the expenditure of energy, usually ATP, to generate an electrochemical gradient. Which of the following pairs of transporters is not an example of secondary active transport? 1. H+ -ATPase and the H+ -nitrate (NO− 3 ) symporter. 2. H+ -ATPase and the H+ -sucrose symporter. 3. Ca2+ -ATPase and the depolarization-activated Ca2+ channel. (Correct Answer) 4. H+ -ATPase and the H+ -sucrose antiporter. Solution: The Ca2+ -ATPase uses ATP directly to pump calcium ions against their gradient, which is primary active transport. The depolarization-activated Ca2+ channel allows ions to flow down their gradient passively, without using ATP. Therefore, they do not fit the mechanism of secondary active transport. Question 4: Osmosis is the term used to describe the diffusion of water. Which of the following statements about diffusion is FALSE? 1 1. A semi-permeable membrane is required for diffusion to occur. 2. High solute concentrations lower the water concentration. 3. Aquaporins facilitate the movement of water across semi-permeable membranes. 4. Water moves from regions of high concentration to regions of low concentration. Correct Answer: A semi-permeable membrane is required for diffusion to occur. Solution: Diffusion is the process where molecules move from an area of higher concentration to an area of lower concentration, and it does not require a membrane. Osmosis, however, specifically involves the movement of water through a semi-permeable membrane. Question 5: Water potential (ψ) is defined as the sum of four component potentials, according to: ψ = ψs + ψp + ψt + ψg . Which of the following statements about ψ is TRUE? 1. ψs increases with increasing solute concentration. 2. ψg contributes significantly to ψ, while ψt does not. 3. ψ can only be a negative value because ψs is always greater than ψp . 4. Water moves from regions of high ψ to regions of low ψ. (Correct Answer) Solution: Water potential (ψ) determines the direction of water movement. Water moves from areas of higher water potential to areas of lower water potential. The components include solute potential (ψs ), pressure potential (ψp ), matric potential (ψt ), and gravitational potential (ψg ). Adding solutes lowers ψs , making it more negative, while positive pressure increases ψ. 2